The invention relates to a ballast water ozone injection method and system. More particularly, the invention relates to a system for using ozone to treat ballast water during loading or discharge of ballast water to or from the ballast tanks of a sea faring vessel.
Ballast water weight is used by sea vessels to compensate for a lack of cargo weight when the cargo load is empty or partially empty. For example in a typical transport operation, a sea vessel docks at a first port where it is loaded with a cargo that the vessel transports to a second port where the cargo is unloaded. The vessel then returns to the first port where it is loaded with another cargo. Typically, the vessel travels empty from the second port back to the first port to pick up another cargo. The vessel is equipped with ballast tanks that can be filled with water to maintain the balance of the vessel on an even keel when it travels empty. Conventional ballast tanks include valves usually mounted over apertures through tank bulkheads. The valves are actuated to move water between and into and out of various ballast tanks to trim the vessel when empty of cargo or when carrying an unevenly distributed cargo.
The vessel fills its ballast tanks by taking on sea water, usually at its cargo discharge port. The sea water is charged into the ballast tanks at the same time that the vessel off loads its cargo. The vessel then travels to its cargo loading port where it takes on cargo while at the same time it empties at least some and typically all of its ballast tanks by discharging the ballast water into the loading port water environment.
The ballast water intake is below the water line of a vessel usually at or near the vessel hull bottom. The ballast water contains algae, zooplankton and other organisms that are indigenous to the cargo discharge port. Significant quantities of these indigenous organisms are loaded into the ballast tanks along with the water. The vessel then transports these organisms to the cargo loading port where the organisms are discharged into the water environment along with discharged ballast water. Some of these organisms may be deleterious to and very much unwanted in the loading port environment. They cause damage to the water environment and replace benthic organisms and clear plankton communities that provide food and larvae for resident native species in overlying waters.
The zebra mussel (Dreissena polymorpha) is an example of an unwanted organism that has been spread by ballast water. The zebra mussel was first found in the mid eighteenth century in the northern Caspian Sea and in the Ural River. Since then, the mussel has spread to other parts of the world by means of ballast water discharge. The mussel was found in the Great Lakes in late 1988. It was first prevalent in Lake Erie. Since then, the mussel has spread into Lake Michigan and into rivers of the Midwest and Northeast.
The mussel has threadlike tentacles that enable it to adhere to any vertical or horizontal surface. It is particularly adherent to the shell of another mussel. It reproduces quickly and in a brief time can obtain population densities in excess of 30,000 mussels per square meter. Stacks of adhering mussels have been known to completely clog water intake orifices and shut down municipal water treatment plants and industrial water systems.
In 1996, Congress passed the National Invasive Species Act (P. L. 104-332) to stem the spread of nonindigenous organisms by ballast water discharge. The act reauthorized the Great Lakes ballast management program and expanded applicability to vessels with ballast tanks. The Act requires the Secretary of Transportation to develop national guidelines to prevent the spread of organisms and their introduction into U.S. waters via ballast water of commercial vessels.
Guidelines developed pursuant to the can require vessels that enter U.S. waters to undertake ballast exchange in the high seas. Ballast water exchange involves replacing coastal water with open-ocean water during a voyage. This process reduces the density of coastal organisms by replacing them with oceanic organisms with a lower probability of survival in near shore waters. However, ballast exchange has two important short-comings. First, the ability to safely conduct ballast water exchange depends upon weather and sea surface conditions, and it is not always possible to perform an exchange. Second, there is still some residual density of coastal organisms in ballast tanks following exchange, so the process is only partly effective.
There is a need for a safe and effective method and system to treat ballast water for discharge into destination water environments.